DC-DC power supply systems may be used to efficiently power modern electronic devices and circuits. For example, light emitting diode (LED) circuits may employ an LED driver to illuminate one or more LEDs. To control the illumination, the LED driver may attempt to regulate output currents and output voltages such that they are at relatively constant levels. While early generation of LED drivers employed open loop driver designs, there may be considerable variations in the forward diode voltage of the LEDs due to process variations, operating temperatures, device ageing, the usage time of the LEDs, the wavelength of the light emitted by the LEDs, and/or other factors. Thus, closed loop drivers can be used to achieve uniform brightness and high efficiency.
Various LED drivers may employ buck, boost, or floating buck power stage topologies. Because some lighting systems may include a large number of LEDs connected in series, the output voltage for a power stage can be several tens of volts. Thus, switches in the power stage can be subjected to considerable voltage stress. As a result, the reliability of the power stage may be impacted.
Furthermore, various LED applications, such as backlights for display devices, may employ multiple “strings” of LEDs. Such systems may use multiple LED drivers. However, the use of multiple LED drivers may result in high costs and/or the use of bulky components, and the efficiency may be relatively poor. Additionally, complex control circuitry may be used to ensure that a relatively constant current is delivered by each power stage for each respective LED string.
In some power stage designs of LED drivers, low-voltage integrated circuit (IC) technologies cannot be used because of the corresponding dielectric breakdown, junction breakdown, hot carriers, and/or other parameters. Instead, high-voltage transistors comprising thick gate oxides and drain extensions may be used. However, high-voltage transistors may result in higher costs as compared to low-voltage transistors.
Various power stage designs may use multiple switches that are connected in series in order to distribute the voltage stress that a single switch would otherwise experience. However, having multiple switches perform the function of a single switch may increase the cost and/or silicon real estate requirements for an LED driver.